Beschreibung: Background and aims Carpobrotus edulis invades coastal areas throughout the world, decreasing plant diversity and hampering restoration efforts by changing soil properties. Some of its effects on soils are known but there is a knowledge gap about the effects in rocky areas and micronutrients that we aimed to fill for dunes and rocky habitats with temperate-humid climate. Methods We compared invaded vs non-invaded paired plots in two dune and two rocky areas by measuring 18 variables in litter and 24 in soils (0–5 and 5–10 cm layers). Results Invasion effects increased with the accumulated alien necromass, decreased with soil depth and are substrate-dependent: soil pH, Al, Fe and P increased in dunes, while these variables and Mg, Cu and Zn decreased in rocky sites. Carpobrotus necromass is richer in Mg and Ca and poorer in Al, Co, Cu, Fe, Ni and Zn than native necromass. Conclusions Invader effects on soils are largely mediated by its necromass, which has contrasting characteristics with the autochthonous necromass. Carpobrotus edulis ability to discriminate against Al uptake, while favouring Mg and Ca uptake, and its lower requirement (or higher resorption) of key micronutrients (Co, Cu, Fe, Ni, Zn) than native vegetation could partly explain its invasiveness.

Beschreibung: Aims The 15 N natural abundance technique is increasingly being used to biological nitrogen (N 2 ) fixation by legume crops, but requires the determination of a ‘B value’ which describes the isotopic fractionation for a given plant species and strain of rhizobium. Most B values in the literature are derived for shoot tissue harvested at mid pod filling, when plant N content is generally at its maximum. However, if legumes are grown as green manure inter-crops and growth is terminated at earlier stages, to obtain accurate values for total N 2 fixed growth-stage specific B values and correction for seed N contributions may be necessary. This study aimed to evaluate the magnitude of the impact of different values of the N content and 15 N abundance of seeds and of B values on the estimates of the proportion of legume N derived from N 2 fixation. Methods We investigated whether B values at pod filling differ from those at earlier growth stages by growing chickpea ( Cicer arietinum ), white lupin ( Lupinus albus ), field pea ( Pisum sativum ) and two faba bean ( Vicia faba ) cultivars, in sand-culture in a glasshouse without N, and quantifying the δ 15 N values of nodules, roots and shoots at five growth stages including mid pod filling as a control. We then used simulations to investigate the degree of error associated with the use of growth stage-inappropriate or B values uncorrected for seed N on estimates of % N derived from atmosphere (%Ndfa). Results While the differences in B values between flowering and pod filling were only statistically significant at P  〈 0.1 for white lupin, there was a trend of declining B value with plant age for chickpea and faba beans. Simulations using data from large (Aguadulce) and small (Fiesta)-seeded faba bean cultivars indicated that the magnitude of potential errors in estimating %Ndfa using B values derived at inappropriate growth stages or uncorrected for seed N content were around 10% at early flowering in both faba bean cultivars and were negligible by late flowering (69 days after sowing). Conclusions Where legumes are grown until flowering or beyond, the magnitude of potential error in estimation of %Ndfa from the use of B values derived at inappropriate growth stages or uncorrected for seed N content is relatively low compared to other sources of error encountered when employing the 15 N natural abundance technique.

Beschreibung: Background and aims The activity of extracellular enzymes is one control on soil organic matter decomposition and serves as a driver of heterotrophic soil respiration. To understand how temperature sensitive enzyme reactions will influence the processing of soil carbon substrates at elevated temperatures, we deployed a passive warming experiment in a deciduous forest with highly invaded understory plant communities and high soil nitrogen concentrations. Methods We seasonally assessed six extracellular enzyme activities and measured soil respiration in the field and in laboratory incubations, to determine if soil carbon use and nutrient cycling responded to 3.5 years of warming. Results Field measurements indicate soil respiration was 24% lower and the production of the recalcitrant C-acquiring enzyme phenoloxidase was also lower in warmed plots during fall and winter. In the spring, phosphate (P) acquiring enzyme activity increased in response to warming. In lab incubations, soil respiration was not different between warmed and control soils. Conclusions Despite minimal changes to C stores after 3.5 years of warming, recalcitrant C-use and nutrient processing enzymes responded differentially to higher temperatures in fall, winter, and spring. This suggests that C- and nutrient cycle responses to warming can change throughout the seasons, perhaps mediated by plant phenological changes.

Beschreibung: Aims This study aims to explain the mechanism of action of allelochemical effect of Chenopodium ambrosioides L. volatile oil on mitochondrial characteristics of receptor plants. Methods This study chose maize ( Zea mays L.), which is widely grown in C. ambrosioides invaded field as the receptor plant, and investigated the allelochemical effect of C. ambrosioides volatile oil and its two main components (α-terpinene and cymene) on maize root tip cells using a suspended gas method and TdT-mediated dUTP Nick-End Labeling (TUNEL) assays. The allelochemical effect on the relative expression of the apoptosis-associated type II Metacaspase gene ZmMCII was measured by quantitative real time polymerase chain reaction (qRT-PCR). The allelochemical effect on mitochondrial characteristics was analyzed by staining assays. Results The results showed that applications of C. ambrosioides volatile oil, α-terpinene, and cymene on maize root tip cells caused membrane lipid peroxidation, increased mitochondrial H 2 O 2 and MDA contents, decreased mitochondrial membrane potential, released mitochondrial Cyt c and Ca 2+ into the cytoplasm, and increased cytosolic Ca 2+ level and expression of the type II Metacaspase gene ZmMCII . These apoptotic effects were time-dependent. Conclusions It suggested that C. ambrosioides volatile allelochemicals induced accumulation of reactive oxygen species (ROS) and triggered mitochondrion-mediated Ca 2+ - and Caspase-dependent apoptosis signaling pathways in receptor plant cells.

Beschreibung: Background and aim Humic substances (HS) are known to influence plant physiological processes, enhancing crop yield, plant growth and nutrient uptake. The present study sought to gain a better understanding of the specific effects of HS application on the abundance of metabolites in plant tissues, using mass spectrometry analyses. Methods Arabidopsis thaliana plants, grown in hydroponic conditions, were treated for 8 h with indole-3-acetic acid (IAA), HS from International Humic Substances Society (IHSS) and HS from earthworm faeces (EF), respectively. Humic substances structural characteristics were analyzed by 1 H NMR an FT-IR spectroscopies. Root and leaf free amino acids, sugar alcohols and carbohydrate contents, and leaf amino acids from protein hydrolysis were identified and quantified by gas chromatography-mass spectrometry (GC/MS), and liquid chromatography-mass spectrometry (LC/MS). Canonical discriminant analysis (CDA) was used to evaluate the influence of the treatments on the studied parameters. Results EF treatment had the highest influence on metabolite profiles compared to the control, IAA and IHSS. CDA analysis highlighted a clear distinction between EF and IHSS plant physiological responses, depending on the different chemical and structural properties of the HS. IAA-treated plants showed no significant difference from the control. Conclusions A better understanding of the specific effects of different HS, also related to their chemical characteristics, might serve as a basis for the identification of marker compounds for HS bioactivity.

Beschreibung: Background and aims Global nitrogen (N) deposition can affect root morphology, anatomy and thus the water uptake by trees. The variation in uptake with the induced changes in root morphology and anatomy, however, is not clear. Methods We grew seedlings of Pinus tabuliformis for two years across an N gradient (0–12 g N m −2 y −1 ) and analysed the associated changes between the root hydraulic conductance (RHC) and the morphology and anatomy of different root orders. Results (1) The RHC increased with N addition and reached the peak at 9 g N m −2 y −1 . (2) The number, length, biomass and mycorrhizal colonization rates of the fine roots (first two order roots) decreased with N addition. (3) The stele diameter and tracheid diameter of the coarse roots (third and higher root orders) increased with N addition. (4) Decreasing root quantity and increasing physiological activity (i.e. RHC and respiration rates) induced by N addition may be a trade-off between root morphology and physiology plastic. Conclusions The morphological, anatomical and physiological responses of the different root orders to N addition increased the water uptake, transport, and whole-seedling growth. These heterogeneous responses should be incorporated into models of root uptake and growth in forest ecosystems.

Beschreibung: Aim A-nine month of field trail was conducted to investigate the accumulation capacity of cadmium and zinc by Arabidopsis halleri spp. germmifera . Methods An experimental site moderately contaminated with Zn and Cd was chosen to evaluate the field traits of seed sowing and seedling transplantation. The exchangeable fraction and total Cd and Zn in the soil and the concentration in harvested plants were determined by inductively coupled plasma mass spectrometer. Results The shoot biomass of A. halleri ssp. germmifera increased after more than 8 months of cultivation, and it was approximately 2.13 t ha −1 in the seedling transplantation group, which was more than three times higher than in the seed sowing group. The lower ratio of Zn/Cd concentration in plants than in the soil and the higher bioaccumulation factor indicated that A. halleri ssp. germmifera has a higher uptake efficiency for Cd than for Zn. In total, A. halleri ssp. germmifera removed 18.20 kg Cd ha −1 and 27.38 kg Zn ha −1 from the soil. After nine months of growth, A. halleri ssp. germmifera extracted (22.87 ± 9.21) % of total Cd concentration and (2.99 ± 0.94) % of total Zn concentration from the soil. However, no significant decrease of exchangeable concentration was shown in soil Cd and Zn, which revealed that the uptake of Cd and Zn by A. halleri ssp. germmifera not only came from exchangeable forms but also from non-exchangeable fractions. Conclusions The results of present study indicated that A. halleri ssp. germmifera can be used to efficiently remove different forms of Cd from contaminated land.

Beschreibung: Backgrounds and aims Soybean yield depends on total N uptake, N use efficiency, and harvest index. Nitrogen uptake relays on biological fixation (BNF) and soil absorption. Usually, BNF is considered a yield-related process. However, there is limited information on whether maximizing percent BNF (%BNF) is actually required to maximize N uptake and yield. Methods Seventy cultivars were evaluated for total N uptake, N use efficiency, and harvest index. Biological N fixation was determined in a subset of cultivars. The harvest index of N derived from atmosphere and from soil was also assessed. Results Yield was positively associated with total N uptake. Highest N uptake was not linked to increased %BNF. An inverse relationship between the amount of BNF (kgBNF) and soil N absorption was observed. Harvest index of N derived from BNF was 85%, while it was 77% for N derived from soil. Conclusions Highest total N uptake was attained by different combinations of kgBNF and mineral soil N absorption. This showed that maximizing %BNF is not required to maximize yield. High %BNF played a pivotal role in determining neutral soil N balance. This is so even though N derived from BNF was more partitioned to seeds than N derived from soil.

Beschreibung: Background and aims The changes in the characteristics of Panicum virgatum , an exotic invasive species, after invading various plant communities on the Loess Plateau in China and the main soil nutrient factors in these communities closely associated with invasion remain unclear. Methods A pot culture experiment was carried out to simulate the changes in photosynthesis, biomass, and biomass allocation in P. virgatum and to identify the main soil nutrient factors in various soils collected from local plant communities. P. virgatum was grown in soils collected from communities of P. virgatum (PS treatment), Setaria viridis (SS treatment), Bothriochloa ischaemum (BS treatment), and Artemisia sacrorum (AS treatment) and in a mixed soil from the communities of S. viridis , B. ischaemum , and A. sacrorum (MS treatment). Results Photosynthesis in P. virgatum differed significantly among the soil treatments. Net photosynthetic rate, stomatal conductance, and photochemical efficiency (Fv/Fm) were highest in PS, whereas single-photon avalanche diode values were highest in PS and SS. The variation of biomass differed significantly in different tissues of P. virgatum in the treatments. Leaf and stem biomasses were highest in PS and SS, and root biomass was highest in PS and MS. Total biomass differed significantly among the treatments, except between BS and MS. Both the leaf to total and stem to total biomass ratios were highest in AS and SS, but the root to total biomass ratio was lowest in these two treatments. A constrained redundancy analysis and a path analysis suggested that the water-soluble nitrate-nitrogen (W-NN) concentration of the soil could significantly affect photosynthesis, biomass, and biomass allocation in P. virgatum . Conclusions Photosynthesis, biomass, and biomass allocation in P. virgatum differed significantly when grown in soils from different local plant communities on the Loess Plateau. The soil W-NN concentration in these local plant communities likely has a large impact on the invasive success of P. virgatum .

Beschreibung: Background and aims Changes in net primary productivity in response to climate change are likely to affect litter inputs to forest soil. However, feedbacks between changes in litter input and soil carbon dynamics remain poorly understood in tropical and subtropical forests. This study aims to test whether the effects of litter manipulation on soil respiration differ between natural and plantation forests. Methods Soil respiration, soil properties, fine root biomass and enzyme activity were measured in adjacent plots with doubling vs. eliminating litter input in both natural and plantation forests of Castanopsis carlesii in southern China. Results After only 3 years of litter manipulation, the magnitude of change in soil respiration was greater in response to a doubling of the litter input (+24%) than to the elimination of litter input (−15%) in the natural forest, possibly due to a positive priming effect on decomposition of soil organic carbon (SOC). The quick and intense priming effect was corroborated by elevated enzyme activities for five of the six enzymes analyzed. In contrast, the response to litter removal (−31%) was greater than the response to litter addition (1%; not significant) in the plantation forest. The lack of positive priming in the plantation forest may be related to its lower soil fertility, which could not meet the demand of soil microbes, and to its high clay content, which protected SOC from microbial attack. The positive priming effect in the natural forest but not plantation forest of C. carlesii is also consistent with the significant declines in total soil carbon observed following litter addition in the natural forest but not the plantation forest. Conclusions Increases in aboveground litter production may trigger priming effects and subsequently transfer more soil carbon to atmospheric CO 2 in the natural forest but not in the plantation forest with low fertility. Changes in litter inputs resulting from global change drivers may have different impacts on natural and plantation forests.